EXPENDABLE EBW FIRING MODULE FOR DETONATING PERFORATING GUN CHARGES

Abstract: An expendable EBW firing module (22) for use with a perforating gun system including a source of DC power (40) at the surface and supplied to the system through a wireline cable (18) interconnected therebetween, without requiring any additional perforating gun hardware. The module includes a high-voltage multiplier circuit (32) for multiplying a first voltage related to the voltage received from the power source (40) by a predetermined multiple to generate a second DC voltage capable of detonating an EBW detonator (22), a firing circuit (39) for receiving the second voltage fromthe multiplier for application to the detonator (22), and an electronic safety circuit (35) interposed between the power source (40) and the multiplier (32) for preventing unintentional activation of the multiplier (32) by stray voltages present at the wellsite. The module is adapted for mounting directly in the interior housing of the perforating gun system adjacent the detonator without protection from the perforating gun charge blast and wherein the module is substantially destroyed upon activation of the detonator.

Description: EXPENDEBLE EBW FIRING MODULE FOR DETONATING PERFORATING GUN CHARGES This invention relates to perforating gun detonation apparatus, and more particularly to exploding bridgewire (EBW) detonators and safe circuits for firing such EBW detonators. A conventional electric detonator of the kind in general use by wireline service companies for use in oil and gas well perforating activities typically contains a bridgewire embedded in an ignition mix, plus a primer charge and a base charge. The primer charge is a sensitive explosive, usually lead azide and the base charge is the same explosive material used in detonating cord and shaped charges, usually RDX or HNS. When sufficient current is applied through the detonator leads to the bridgewire it ignites the ignition mix, which in turn ignites the primer charge. The exploding primer charge causes the base charge to detonate. The main drawbacks of such electric detonators are: 1. . They contain sensitive primary explosives, and must be handled carefully to avoid accidental initiation by mechanical impact; and 2. They are easily fired electrically, requiring only the application of 0.5 A or less for a few milliseconds. Accordingly, they are particularly susceptible to any source that could provide this power accidentially, such as electric welding equipment, radio transmitters, cathodic protection systems and faulty rig machinery and equipment. To protect against such spurious electrical power, all possible equipment and machines that could produce such stray power often had to be shut down for extended periods, and the wellhead and rig structure monitored for stray voltages. By contrast, Exploding Bridgewire (EBW) detonators contain no primary explosive, which makes them insensitive to initiation by mechanical impact and therefore safer to handle than conventional detonators. In addition, they are immune to initiation by the external power sources usually on the well or rig site. However, to fire an EBW detonator successfully requires the use of a specialized electronic circuit. That electronic circuit can pick up spurious AC, radio frequency (RF) and DC voltages from the many rig sources named above, including lightning strikes that can accidentially cause the EBW detonator to be fired. Accordingly, it is necessary to design the electronic firing circuits for EBW detonators to include safety circuits for isolating the detonator firing circuit from such spurious voltages to prevent accidental detonation of the perforating gun charges. The present invention remedies the problems of the prior art by providing a compact expendable EBW firing module for use in connection with a conventional perforating gun system, including a source of DC power at the surface and supplied to the perforating gun system through a wireline cable interconnected thereto, without requiring any additional perforating gun hardware, including a high-voltage multiplier circuit for multiplying a first voltage related to the voltage received from the DC power source by a predetermined multiple to generate a second DC voltage capable of detonating an EBW detonator, a firing circuit for receiving said second DC voltage from the multiplier circuit for application to the EBW detonator, and an electronic safety circuit interposed between the DC power supply at the surface with the multiplier circuit for preventing unintentional activation of the multiplier circuit by stary AC/RF and DC voltages present at the wellsite. The expendable EBW firing module is adapted for mounting directly in the interior housing of the conventional perforating gun system directly adjacent the EBW detonator without protection from the perforating gun charge blast and said expendable EBW firing module is substantially destroyed upon activation of the adjacent EBW detonator. In order that the manner in which the above-recited principles and features of the invention are attained can be understood in detail, a more particular description of the invention may be had by reference to specific embodiments thereof which are illustrated in the accompanying drawings, which drawings form a part of this specification. In the drawings: Fig. 1 is an illustrative drawing showing a wireline perforating tool disposed in a wellbore and utilizing the expendable EBW firing module according to the present invention. Fig. 2 is a block diagram showing the major assemblies of the wireline perforating tool utilizing the expendable EBW firing module according to the present invention. Fig. 3 is a detailed schematic diagram of the preferred embodiment of the expendable EBW firing module according to the present invention. Fig. 4 is a detailed schematic diagram of another embodiment of the expendable EBW firing module according to the present invention. Fig. 5 is a vertical diagrammatic view, partly in cross- section, of a wireline perforating gun system utilizing the expendable EBW firing module in accordance with this invention. Fig. 6 is a cross-sectional view of one embodiment of protective packaging for the expendable EBW firing module. Referring to Figs. 1 and 2, a wireline perforating gun system 10, including the expendable EBW firing module24, is shown disposed in a borehole 14 that has been drilled in earth formation 12. The perforating gun tool 10 is shown spaced adjacent steel casing 16 that has been set in the borehole 14 adjacent a formation of interest 13. The tool 10 is supported by a conventional single- or multi-conductor wireline cable 18 that travels over a sheave 26 and is spooled onto a winch drum 28. The perforating tool 10 is raised and lowered in the borehole 14 by the action of the cable drum 28 and the "spooling out" of the cable 18 to lower the gun system 10 in the borehole, or the "spooling in" of cable 18 to raise the perforating gun system 10 in the borehole 14. Depth measurements are made from the travel of the wireline cable 18 as it passes over the sheave 26 and communicated to the surface control equipment 30 via cable or conductor 32. Electrical power for operating the perforating gun system 10, including the necessary control signals for firing the tool, are applied through cable 18 from the control equipment 30. The perforating gun system 10 includes a perforating gun section 20, an electronic bridge wire (EBW) detonator and booster section 22, the expendable EBW firing module 24 according to the present invention cooperating with the EBW section and a cablehead 25 interconnected to the cable 18 and the control panel 30. As will hereinafter be described in greater detail, and as more particularly shown in Fig. 2, the expendable EBW firing module 24 comprises a safety circuit 35, a voltage multiplier circuit 37 and a firing circuit as more particularly shown in Fig. 3. The expendable EBW firing module 24 receives DC power for operating the EBW and booster section 22 for firing the perforating gun system 20 from a DC power supply 40 disposed in the surface control equipment 30 transmitted via the single- or multi-conductor cable 18 and cablehead 25. Referring now to Figs. 1, 2and 3, the operation of the preferred embodiment of the expendable EBW firing module 24 will be described in detail. DC electrical power is applied from the DC power supply 40 in the surface equipment 30 through the cable 18 and cablehead 25 to the input of the safety circuit 35. The DC power (200 VDC) is applied to one side of a surge voltage protector (SVP) 41, the SVP 41 rated at 600 volts. The SVP will conduct and connect the input of circuit 35 directly to ground potential (the perforating gun housing) at 48 in the event of an applied voltage surge in excess of 600 VDC, such as in the case of a lightning strike nearby to the perforating gun system 10 or other DC power interference at the well site. The 200 VDC applied across the SVP 41 is also applied across a resistor 44 and a series connected LED 46, a capacitor bank 50-50' and to the positive side of a diode 52. The capacitor bank 50-50' appears as an open circuit to DC power, but will react with radio frequency (RF) and AC power as a low impedance path to shunt any RF/AC applied as an input to the circuit 35 to ground at 48. While the capacitor bank 50-50' is shown comprising several capacitors in series, the capacitor bank could be repleced with a single capacitor that is rated the same as the combined capacitance of the bank 50-50'. Resistor 44 acts as a bleed resistor for the capacitor bank 50-50', and as a current limiting resistor for the LED 46. The fuse 42 is rated at 125 mA and any significant stray RF or AC voltage will cause a current in excess of the rating of fuse 42 which will blow the fuse and disable the circuit. Such AC and/or RF inputs might be caused by adjacent power generating machinery, radio transmitters, radar equipment, faulty rig wiring or equipment or other like sources that may be present at the well site. The LED will conduct when any current is flowing through resistor 44, and is particularly useful as a power indicator when testing the circuit on the surface prior to lowering the perforating tool into the well bore. As power is applied to the circuit 35, the diode 52 conducts and applies the DC voltage to the anode of the SCR 58. As soon as the voltage across the Zener diodes 56 and 56' reaches 150 VDC, the SCR 58 is switched on and acts as a basic "short circuit" to permit current to pass without offering any significant impedance. The SCR 58 thus acts as a "switch" to sharply turn "on" when 150 VDC appears across the anode and gate legs of the SCR. This acts as a safety feature to prevent other stray DC voltages under 150 VDC, such as may be caused by a welding machine or other DC machinery at the well site, from passing through to the voltage multiplier circuit 37 and activating it. The resistor 60 is a bias resistor to achieve positive shut-off of the SCR when the applied voltage is removed from the anode. The remaining components of the safety circuit 35 comprise a self-triggering multivibrator- circuit for applying an AC input signal to the voltage multiplier circuit 37 as will hereinafter be further described. The heart of the multivibrator circuit are the pair of transistors 66 and 68, the collectors of each of which are connected as an input to the multiplier circuit 37 through conductors, 80 and 78, respectively. The resistors 62 and 64 are current limiting resistors, and resistors 70 and 72 act as biasing resistors for the base inputs 66' and 68' of the transistors 66 and 68, respectively. The capacitors 74-74' and 76-76' couple the bases 66' and 68' of each transistor to the collector of the other transistor. The output of the multivibrator circuit is an approximate sine wave that is applied to the input of the voltage multiplier circuit 37 via conductors 78 and 80. The voltage multiplier circuit 37 is a conventional stacked voltage doubler circuit that will receive an input of 200 VAC and multiply the voltage by a predetermined value, in this case eight, and generate an output of 1600 VDC applied through diode 99 and input resistor 104, to resistor 100 in parallel with capacitor 102 of the firing circuit 39. The resistor 100 is a bleed resistor for the capacitor 102 while resistor 104 acts as a current limiting resistor. In series with resistor 104 is another SVP 106, which is rated at 1500 VDC, and which will conduct when capacitor 102 has reached a voltage of 1500 VDC to apply the 1500 VDC in a time interval of 1 uSec to the output of the firing circuit 39 to the EBW and booster in 22 for actuating the EBW and firing the perforating guns. A resistor 108 is placed in parallel with SVP 106 between the output of the circuit 39 and the capacitor 102 for acting as a bleed resistor for capacitor 102 and to permit direct voltage reading across the firing storage capacitor 102 for testing purposes. During testing at the surface prior to the time the expendable EBW firing module24 is attached into the circuit of the perforating gun system 10, a load resistor (or a dummy EBW) may be tied to the output leads of the firing circuit 39 and the rated 200 VDC applied to the input of the safety circuit 35. A test voltmeter may also be attached across the output leads of the circuit 39 and a measurement of the voltage appearing across capacitor 102 may be made to verify that the circuit is functioning properly. The inductor 54 functions to protect the multivibrator circuit described above from large voltage spikes that may be conducted through the grounding connections of the tool when the capacitor 102 is discharged. This protection is only necessary during testing, since the expendable EBW firing modulewill be damaged beyond repair upon actual detonation of the EBW and the firing of the perforating guns. Referring now to Figs. 1, 2 and 4, the operation of another embodiment of the expendable EBW firing module24 will be described in detail. DC electrical power is applied from the DC power supply 40 in the surface equipment 30 through the cable 18 and cablehead 25 to the input of the safety circuit 35'. The DC power (200 VDC) is applied to one side of a surge voltage protector (SVP) 141, the SVP 141 being rated at 600 volts, and functioning in the same manner as SVP 41 in the circuit of Fig. 3 as hereinabove described to conduct and connect the input of circuit 35 directly to ground potential (the perforating gun housing) at 148 in the event of an applied voltage surge in excess of 600 VDC, such as in the case of a lightning strike nearby to the perforating gun system 10 or other DC power interference at the well site. The 200 VDC applied across the SVP 141 is also applied across a capacitor 150 and to a fuse 142. The capacitor 150 appears as an open circuit to DC power, but will react with radio frequency (RF) power to create a low impedance path to shunt RF power applied as an input to the circuit 35 to ground at 48. Diodes 152 and 153 conduct and apply the DC power to an AC voltage shunt circuit comprising capacitor 144, and cascaded transistors 146 and 149. AC current will pass through the capacitor 144 and be applied to the base of the first transistor 146 via lead 147, causing the transistor to conduct. When transistor 146 conducts, the second transistor 149 is switched on, causing the applied voltage to be shunted to ground. With an AC voltage of about 30 V and 60 Hz, enough current will flow through the transistor 149 to blow the fuse 142, thus disabling the circuit. Such AC and/or RF inputs might be caused by adjacent power generating machinery, radio transmitters, radar equipment, faulty rig wiring or equipment or other like sources that may be at the well site. Resistors 156 and 157 act as current limiting resistors to prevent the activation of the IC 158 until approximately 130 VDC has been applied from power supply 40. The Zener diodes 169, 170 and 171 act to prevent voltages below approximately 150 VDC from being passed to the voltage multiplier circuit 37'. The resistors and capacitors 159, 160, 161, 162, 163 and 164 form other resistive and capacitance values for biasing the selected IC circuit 158 and to preselect the frequency and the pulse width of the generated pulse signal train for applying AC triggering pulses to the to transistor 168 as will hereinafter be further described. The pulse train output of the IC circuit 158 is applied through current limiting resistor 165 to the base of transistor 168 which conducts on the occurrence of each pulse. A Zener diode 166 is interconnected between the base and emitter of the transistor 168 to prevent an overvoltage appearing thereacross. The transistor 168 acts as a switch only to rapidly pulse the current through the inductor 172. The rapidly rising and collapsing electromagnetic fields in inductor 172 caused by the pulsed current therethrough generate a series of high-voltage spikes, which act as the input of the stacked voltage doubler circuit as hereinabove described. The voltage multiplier circuit 37 is a conventional stacked voltage doubler circuit that will receive the output across inductor 172 and multiply this voltage by a predetermined multiplier factor to generate an output of 1600 VDC applied through diode 199 as an input to resistor 204, and to resistor 200 in parallel with capacitor 202 of the firing circuit 39' . The resistor 200 is a bleed resistor for the capacitor 202 while resistor 204 acts as a current limiting resistor. In series with resistor 204 is another SVP 206, which is rated at 1500 VDC, and which will conduct when capacitor 202 has reached a voltage of 1500 VDC to apply the 1500 VDC in a time interval of 1 uSec to the output of the firing circuit 39' to the EBW and booster in 22 for actuating the EBW and firing the perforating guns. A resistor 208 is placed in parallel with SVP 206 between the output of the circuit 39 and the capacitor 202 for acting as a bleed resistor for capacitor 202 and to permit direct voltage reading across the firing storage capacitor 202 for testing purposes. During testing at the surface prior to the time the expendable EBW firing module 24 is attached into the circuit of the perforating gun system 10, a load resistor (or a dummy EBW) may be tied to the output leads of the firing circuit 39 and the rated 200 VDC applied to the input of the safety circuit 35. A test voltmeter may also be attached across the output leads of the circuit 39 and a measurement of the voltage appearing across capacitor 202 may be made to verify that the circuit is functioning properly. The inductor 154 functions in the same manner as inductor 54 as hereinabove described in connection with Fig. 3 for protecting the IC circuit 158 from large voltage spikes that may be conducted through the grounding connections of the tool when the capacitor 202 is discharged. As described above, this protection is only necessary during testing, since the expendable EBW firing modulewill be damaged beyond repair upon actual detonation of the EBW detonator. Components for the circuits described above are given in the following table: Table 1 Component Values Ref. No. Component 41, 141 SVP 600 VDC 42 Fuse 125 ma 142 Fuse 100 ma 50, 50' Capacitor, 47 uF 52, 152, 153, 86, 87, 88, 89, 90, 91, Diode 1N4249 1000 V, 1 A 92, 93, 99, 186, 187, 188,189, 190, 191 & 199 54, 154 Inductor, 1000 uH 56, 56' Zener diode, 75 V 58 SCR, MCR 100-6 60 Resistor, 10 K 62, 64 24.9 K 66, 68 Transistor, MJE13007 70, 72 Resistor 464 K 74, 74' 76 & 76' Capacitor, 0.001 uF 82, 83, 84, 85, 86, 94, 95, 96, 97, 98, Capacitor, 0.01 uF 164, 182, 183, 184, 194, 195, 196 & 198 100, 200 Resistor, 390 M 102 Capacitor, 0.32 uF, 2000 V 202 Capacitor, 0.27 uF, 2000 V 104, 202 Resistor, 150 K 106, 206 SVP, 1500 VDC 108, 208 Resistor, 390 M 144 Capacitor, 0.01 uF 146, 149 & 168 Transistor, MPSA42 156 Resistor, 30 K 157 Resistor, 36 K 158 Integrated Circuit (IC) TL494 159 Resistor, 10 K 160 Resistor, 45.3 K 162 Capacitor, 1 uF 163 Resistor, 37.4 K 165 Resistor, IK 166, 169, 170 & 171 Zener diode, 51 V 172 Inductor, 50 mH Referring now to Figs. 1, 2 and 5, a portion of the perforating gun system 10 is shown comprising a portion of the perforating gun section 20, showing the typical perforating shaped charges 225 supported by a charge carrier (not shown for simplicity) distributed vertically in the gun section 20. A hollow nose plug 20' is shown attached to the lower end of the perforating gun section 20 by means of a threaded connection 21. An electrical power conductor from cablehead 25 (Figs. 1 and 2) and a primacord 225 interconnecting the shaped charges 235 terminate below a bulkhead 227 at the end of the gun section 20. The expendable EBW firing module 24 is connected to the power conductor (+) and to the gun section body for ground (-), and the EBW and booster 22 are connected to the primacord. A pair of conductors 228 and 230 connect the output of the firing circuit 39 of the expendable EBW firing module 24 to the EBW 22. When the expendable EBW firing module 24 detonates the EBW to set off the shaped charges 235 of the perforating gun section 20, the force of the EBW and booster charge 22 blast will substantially destroy the module 24. When the perforating gun is returned to the surface, the gun section 20 will be replaced, new charges 235 loaded, and a new expendable EBW firing module 24 and EBW and booster charge 22 mounted and interconnected for firing the perforating charges as hereinabove described. Of course, the expendable EBW firing module 24 and the associated EBW 22 may be mounted either below the gun section 20 as shown in Fig. 5, or above the gun section as preferred. If a second gun section is being carried in the perforating gun system for perforating multiple formation vertical intervals, a second expendable EBW firing module24 may be attached to the electrical power conductor 226 for the second device with the (+) and (-) terminals reversed and the second circuit 24 will fire upon the application of a negative DC power input. The circuits 35, 37 and 39 that make up the expendable EBW firing module 24 are mounted on a single circuit board and comprise a size of approximately 5 inches by 5/8 inches, and may be packaged in a selected packaging material for protecting the expendable module during transit and handling. Fig. 6 shows an example of such packaging, in wich the module 24 is shown comprising a single circuit board 250 upon which is mounted electrical circuit components such as shown at 252 is encased in a plastic resin materail 254. The plastic resin material 254 may also comprise any other selected packaging material that will serve the necessary purpose of protecting the circuit board 250 and components 252, such as a plastic tubing "shrink-wrapped" onto the circuit board or mounted within a heavier plastic tubing. A pair of conductors 256 and 258 would extend from the module 24 for attaching the module to the power input cord 226 (Fig. 5) and the tool housing and for interconnection to the EBW and booster charge section 22. Numerous variations and modifications may be made in the structure herein described without departing from the present inevntion. Accordingly, it should be claerly understood that the forms of the invention herein described and shown in the figures of the accompanying drawings are illustrative only and are not intended to limit the scope of the invention.

Claims: CLAIMS 1. A compact expendable EBW firing module for use in connection with a conventional perforating gun system, including a source of DC power at the surface and supplied to the perforating gun system through a wireline cable interconnected thereto, without requiring any additional perforating gun hardware, comprising a high-voltage multiplier circuit for multiplying a first voltage related to the voltage received from the DC power source by a predetermined multiple to generate a second DC voltage capable of detonating an EBW detonator, a firing circuit for receiving said second DC voltage from said multiplier circuit for application to the EBW detonator, and an electronic safety circuit interposed between the DC power supply at the surface with said multiplier circuit for preventing unintentional activation of the multiplier circuit by stary AC/RF and DC voltages present at the wellsite, wherein said expendable module is adapted for mounting directly in the interior housing of the conventional perforating gun system directly adjacent the EBW detonator without protection from the perforating gun charge blast and said expendable EBW firing module is substantially destroyed upon activation of the adjacent EBW detonator.

Inventors: ELLIS JAMES, REID NICHOLAS B, ELLIS, JAMES, REID, NICHOLAS, B.
Applicants: WESTERN ATLAS INT INC, WESTERN ATLAS INTERNATIONAL, INC.
Application year: 1994
Main classification: F42C21
IPC codes: E21B43, F42D1